The present invention relates to methods of forming and placing proppant pillars into a subterranean formation.
Subterranean wells (e.g., hydrocarbon producing wells, water producing wells, or injection wells) are often stimulated by hydraulic fracturing treatments. In traditional hydraulic fracturing treatments, a treatment fluid, which may also function simultaneously or subsequently as a carrier fluid, is pumped into a portion of a subterranean formation at a rate and pressure sufficient to break down the formation and create one or more fractures therein. Typically, particulate solids, such as graded sand, are suspended in a portion of the treatment fluid and then deposited into the fractures. These particulate solids, or “proppant particulates,” serve to prevent the fractures from fully closing once the hydraulic pressure is removed. By keeping the fractures from fully closing, the proppant particulates aid in forming conductive paths through which fluids produced from the formation may flow.
The degree of success of a fracturing operation depends, at least in part, upon fracture porosity and conductivity once the fracturing operation is complete and production is begun. Traditional fracturing operations place a large volume of proppant particulates into a fracture to form a “proppant pack” in order to ensure that the fracture does not close completely upon removing the hydraulic pressure. The ability of proppant particulates to maintain a fracture open depends upon the ability of the proppant particulates to withstand fracture closure and, therefore, is typically proportional to the volume of proppant particulates placed in the fracture. The porosity of a proppant pack within a fracture is related to the interconnected interstitial spaces between abutting proppant particulates. Thus, the fracture porosity is closely related to the strength of the placed proppant particulates and often tight proppant packs are unable to produce highly conductive channels within a fracture, while reducing the volume of the proppant particulates is unable to withstand fracture closures.
One way proposed to combat the problems inherent in tight proppant packs involves the use of proppant pillars. As used herein, the term “proppant pillar” refers to a coherent body of consolidated proppant particulates that generally remain a coherent body and do not disperse into smaller bodies without the application of shear. Proppant pillars are comprised of a plurality of proppant particulates formed into a tight cluster and are capable of withstanding fracture closure pressures. The use of proppant pillars, therefore, may reduce or eliminate the likelihood of partial or complete fracture closure. The proppant pillars placed into a fracture do not abut together perfectly and therefore may achieve infinite conductivity channels (e.g., unobstructed pathways) for produced fluid flow. However, while proppant pillars can overcome the issues associated with tight proppant packs, in practice several issues may prevent their optimal performance. Specifically, while proppant pillars do not disperse into smaller bodies in the absence of shear, they often encounter shear when being placed into a subterranean formation, particularly when encountering fracture closure stresses. Thus, the proppant pillars may be of a sub-optimal size due to dispersion after fracture closure, such that they are unable to maintain fracture conductivity. Therefore, a method of forming and placing proppant pillars into a subterranean formation such that they do not disperse into smaller bodies may be of benefit to one of ordinary skill in the art.